The Kollel wrote (Insights to the Daf 1:(b)), "Another weakness in the proof from Yehoshafat is that we find that Achav repented from his evil ways (I Melachim 21:29) *before* the incident of the meal with Yehoshafat took place! Perhaps Achav remained steadfast in his Teshuvah and never returned to his evil ways, and, therefore, he was no longer considered a Mumar l'Avodah Zarah. (OR HA'CHAYIM, in CHEFETZ HASH-M.) (See MITZPEH EISAN, who discusses how Rav Anan cites proof from Yehoshafat in the first place.)
Regarding the fact that Yehoshafat ate from the shechita of Achav AFTER Achav did teshuva, how can we refer to it as teshuva when Achav did not remove the avoda zarah from the land and did not remove the obstacles to go to Yerushalayim and the egels??
Thanks,
David Goldman
Despite the Or ha'Chayim's claim that Achav did Teshuvah, we must remember that the Gemara still refers to him as a Mumar la'Avodah Zarah, as the Or ha'Chayim himself points out. Perhaps the Gemara's reason is based on your question.
On the other hand, to understand the Or ha'Chayim's contention, perhaps someone who is genuinely sorry for having sinned, and who no longer continues to sin, loses his title of 'Mumar', even though he did not rectify what he did wrong.
The Or ha'Chayim however, is difficult to understand in light of the opening Mishnah of Chelek (the eleventh Perek of Sanhedrin), which lists Achav among the three kings who lost their portion in the World to Come. If he genuinely did Teshuvah, then why will the principle that 'Nothing stands in the way of Teshuvah' not apply here?
Maybe it is because he caused many others to sin, and Chazal have said in similar circumstances "so that his disciples should not sit in Gehinom, while he sits in Gan Eden'.
Be'Virchas Kol Tuv
Eliezer Chrysler